Recently I've switched through a lot of different OS setups and my projects list in Spacemacs was bloated.
Some projects were from MacOS, others were from Windows. All of them were not existed anymore.
I've tried to find a file where Emacs (Spacemacs) stores list of projects but I've found even better elisp function for this.
Just call `M-x projectile-cleanup-known-projects` and every path (project) that is not exists on your current machine will be removed from the list of known projects.
Glad there is such function and my *spacemacs* buffer looks much much better now